Keck again holds the record, for the moment at least, of the farthest galaxy ever observed. It is a record that we have been passing back and forth with the neighboring Subaru Telescope for some years now. We currently have the advantage of MOSFIRE, a fantastic spectrograph to discover these objects. I expect our hold on this title will be transitory, there are candidate objects that may even be somewhat further away and back in time.
Why try to observe these galaxies? They tell us a great deal about the formation of the first stars and galaxies after what astronomers call the “Dark Ages”, a period of time after the Big Bang when light could not travel through the galaxy, absorbed by a fog of neutral hydrogen. These first stars and galaxies ionized this hydrogen, creating the transparent universe we see today. By studying these galaxies we learn a great deal about how the universe we see today came to be.
An international team of astronomers, led by Yale and the University of California, Santa Cruz, pushed back the cosmic frontier of galaxy exploration to a time when the Universe was only five percent of its present age. The team discovered an exceptionally luminous galaxy more than 13 billion years in the past and determined its exact distance from Earth using the powerful MOSFIRE instrument on the 10-meter Keck I telescope at the W. M. Keck Observatory in Hawaii. These observations confirmed it to be the most distant galaxy ever measured, setting a new record. The findings are being published in Astrophysical Journal Letters today.
The galaxy, EGS-zs8-1, is one of the brightest and most massive objects in the early universe and was originally identified based on its particular colors in images from NASA’s Hubble and Spitzer Space Telescopes.
“While we saw the galaxy as it was 13 billion years ago, it had already built more than 15 percent of the mass of our own Milky Way today,” said Pascal Oesch of the Yale University, the lead author of the study. “But it had only 670 million years to do so. The universe was still very young then.” The new distance measurement also enabled the astronomers to determine that EGS-zs8-1 was still forming stars very rapidly, about 80 times faster than our galaxy today.
Only a handful of galaxies currently have accurate distances measured in this epoch of the Universe and none younger than this.
“Every confirmation adds another piece to the puzzle of how the first generations of galaxies formed in the early universe,” said Pieter van Dokkum of the Yale University, second author of the study. “Only the largest telescopes are powerful enough to reach to these large distances.”
The discovery was only possible thanks to the relatively new MOSFIRE instrument on the Keck I telescope, which allows astronomers to efficiently study several galaxies at the same time.
Measuring galaxies at these extreme distances and characterizing their properties is a main goal of astronomy over the next decade. The observations see EGS-zs8-1 at a time when the Universe was undergoing very important changes: the hydrogen between galaxies was transitioning from a neutral to an ionized state.
“It appears that the young stars in the early galaxies like EGS-zs8-1 were the main drivers for this transition called reionization”, said Rychard Bouwens of the Leiden Observatory, co-author of the study.
These new Keck Observatory, Hubble, and Spitzer observations together also pose new questions. They confirm that massive galaxies already existed early in the history of the Universe, but that their physical properties were very different from galaxies seen around us today. Astronomers now have very strong evidence that the peculiar colors of early galaxies seen in the Spitzer Space Telescope images originate from a very rapid formation of massive, young stars, which interacted with the primordial gas in these galaxies.